FIG. 1 illustrates a conventional prior art low-cost single-panel LCD projection system 10 that uses a brute force method to create color.
An illumination system 12 with a light source 14 provide uniform illumination of an multi-color liquid crystal display (LCD) 16, which has embedded color filters 18R, 18G, and 18B corresponding to red, green and blue primary color components. Color filters 18R, 18G, and 18B are aligned over individual sub-pixels (not shown) of LCD 16.
Each subpixel is independently addressable so that the liquid crystal molecules of LCD 16 can be driven to certain tilt angles as is known in the art, to effect varying degrees of light transmission intensity. With appropriate associated polarizers, for example, this varies the red, green and blue subpixel intensities to provide a generally full color image. Projection optics 20, which are represented schematically, project the color image to a display screen 22.
Problems with this brute force approach are a low transmission rate, especially when color filters are highly saturated, so as to yield good (i.e. pure) color primaries, or poor color saturation (yielding impure color primaries) to increase transmission rate. In addition, this approach also causes heating within the LCD panel due to absorption by the color filters. Typically, the absorption of green light by the red color component filter 18R is inevitable. Likewise, a blue color component filter 18B passes mainly just blue light and green filter 18G passes mainly just green light. Thus the majority of the illumination light (i.e., ⅔ of total) is absorbed by the color component filters 18R, 18G, and 18B. Simplified diagrams of light spectra illustrate generally a spectrum 30 for polychromatic (“white”) light provided by light source 14 and the resulting spectra 32, 34, and 36 of respective red, green, and blue color components generated by projection system 10.
The present invention addresses all three of these problems, by providing a color prefilter, positioned between the light source and the LCD panel, to shape the spectrum of the illumination so as to increase the relative panel transmission and to reduce the heat absorption within the LCD embedded color filters.
The present invention includes a single-panel LCD projection system that includes a color prefilter positioned between an illumination system and a multi-color liquid crystal display (LCD) having an associated polarizer and analyzer. The color prefilter functions to shape the spectrum of illumination provided by the illumination system so as to increase relative panel transmission and to reduce heat absorption by color component filters (e.g., red, green and blue) incorporated in the LCD.
The color prefilter is selected to eliminate from or greatly reduce in the illumination light the intensity of certain wavebands that do not materially contribute to generating pure primary colors. A consequence of adding the color prefilter is that the LCD color component filters can be desaturated and the overall total transmission of the projection system can be improved. In one implementation, the color prefilter is able to remove the wavebands of highest absorption by the LCD color component filters before such light strikes the LCD, so that there is less heat build-up in the LCD.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.